1. Field of the Invention
The present invention relates to ultrasound therapy and imaging systems, and in particular to a method and system for noninvasive face lifts and deep tissue tightening.
2. Description of the Related Art
Coarse sagging of the skin and facial musculature occurs gradually over time due to gravity and chronic changes in connective tissue generally associated with aging. Invasive surgical treatment to tighten such tissues is common, for example by facelift procedures. In these treatments for connective tissue sagging, a portion of the tissue is usually removed, and sutures or other fasteners are used to suspend the sagging tissue structures. On the face, the Superficial Muscular Aponeurosis System (SMAS) forms a continuous layer superficial to the muscles of facial expression and beneath the skin and subcutaneous fat. Conventional face lift operations involve suspension of the SMAS through such suture and fastener procedures.
No present procedures have been developed yet, which provide the combination of targeted, precise, local heating to a specified temperature region capable of inducing ablation (thermal injury) to underlying skin and subcutaneous fat. Attempts have included the use of radio frequency (RF) devices that have been used to produce heating and shrinkage of skin on the face with some limited success as a non-invasive alternative to surgical lifting procedures. However, RF is a dispersive form of energy deposition. RF energy is impossible to control precisely within the heated tissue volume and depth, because resistive heating of tissues by RF energy occurs along the entire path of electrical conduction through tissues. Another restriction of RF energy for non-invasive tightening of the SMAS is unwanted destruction of the overlying fat and skin layers. The electric impedance to RF within fat, overlying the suspensory connective structures intended for shrinking, leads to higher temperatures in the fat than in the target suspensory structures. Similarly, mid-infrared lasers and other light sources have been used to non-invasively heat and shrink connective tissues of the dermis, again with limited success. However, light is not capable of non-invasive treatment of SMAS because light does not penetrate deeply enough to produce local heating there. Below a depth of approximately 1 mm, light energy is multiply scattered and cannot be focused to achieve precise local heating.